(1):
(a.) Of or pertaining to a profession, or calling; conforming to the rules or standards of a profession; following a profession; as, professional knowledge; professional conduct.
(2):
(a.) Engaged in by professionals; as, a professional race; - opposed to amateur.
(3):
(n.) A person who prosecutes anything professionally, or for a livelihood, and not in the character of an amateur; a professional worker.